1. Field of the Invention
The present invention relates to an yttria sintered body, having an excellent corrosion resistance to halogen-based corrosive gases and plasma, and adapted for use in a plasma process apparatus for manufacturing semiconductors and liquid crystal devices.
2. Description of the Background Art
In semiconductor manufacturing apparatuses, component members formed by silicon, quartz glass or silicon carbide are frequently utilized (see Japanese Patent Unexamined Publication JP-A-2002-15619). Such materials, being principally constituted of Si, C and O which are constituent elements of a semiconductor wafer or the like to be manufactured and being obtainable with a high purity. Thus, there is an advantage of not contaminating the wafer even when the component contacts with the wafer or even when a vapor of the constituent evaporates from such component members.
However, such materials involve a drawback of undergoing a significant corrosion by a halogen-based gas, particularly a fluorine-based gas, and is therefore unsuitable as a member for an apparatus to be used in an etching process, a CVD film forming process or an ashing process for removing a resist material, principally executed by a plasma process utilizing a highly reactive halogen-based corrosive gas such as fluorine or chlorine.
Therefore, for members to be exposed to halogen plasma in such processes, ceramics such as highly pure alumina, aluminum nitride, yttria or YAG are utilized.
Among these materials, yttria is attracting attention because of an excellent plasma resistance thereof.
For example, Japanese Patent Unexamined Publication JP-A-2003-234300 discloses that a porous sintered body of yttria ceramics is usable in a plasma process apparatus.
On the other hand, for use as a component member in a plasma process apparatus, a material, having an excellent plasma resistance and also having a low volume resistivity or a volume resistivity arbitrarily controllable according to the condition of use, has been desired.
For reducing the volume resistivity of such ceramics, for example, it is conceivable “to add to alumina, a powder of a compound containing an alkali metal or a transition metal, or a powder of titanium oxide”, or “to add, to a high-resistance ceramics as described above, a metal oxide such as titanium oxide or tungsten oxide, a metal nitride such as titanium nitride, or a metal carbide such as titanium carbide, tungsten carbide or silicon carbide, showing an conductivity”.
JP-A-7-233434 discloses a corrosion resistant material in which particles of a metal oxide such as yttria are dispersed in a proportion of 50 vol % or less in a matrix of a high-melting metal such as tungsten. Such material is intended, as a material resistant to corrosion by a rare earth metal such as yttrium in a molten state, for a component member such as a crucible, coming into contact with such molten rare earth metal.
The aforementioned method, when used in reducing the volume resistivity of ceramics of a high plasma resistance such as high purity alumina, aluminum nitride, yttria or YAG, results in a deterioration of the plasma resistance and in an inclusion of impurity elements leading to a contamination of the wafer, and cannot therefore be considered as a practically acceptable method.
Also in the member formed by the ceramics as mentioned above, the volume resistivity is also influenced by a pore rate of the material, and a dense sintered body is desirable for reducing the volume resistivity. For this reason, a sintering process with a special method under a high-temperature environment such as hot pressing (HP) or hot isostatic pressing (HIP) is required. However, the manufacture of a large-sized member matching the increasing diameter of the wafer becomes very costly.
Yttria ceramics, though excellent in the plasma resistance as described above, there are drawbacks in comparison with other ceramics such as alumina, of a lower strength, a lower thermal shock resistance and a possibility of breakage by a thermal stress depending on temperature conditions, when employed as a component member of a semiconductor manufacturing apparatus. More specifically, it can be used without difficulty under a temperature of about 50° C., but shows a high probability of breakage when used in a high temperature range of 200° C. or higher.
Therefore, for use as a component member of a plasma process apparatus in semiconductor manufacture or the like, a yttria sintered body capable of showing a thermal shock resistance usable under a high temperature condition of 200° C. or higher, without deteriorating the excellent plasma resistance of yttria, is being desired.